We are in the same situation.
Mr W just turned 4 and his reading has exploded. He is reading Magic Tree house now.
He is in an "advanced" academic PreK with older kids and they are still on letters. He is complaining of being bored and he no longer wants to go there and wants to stay at home where he can read and learn about stuff.
He wants to focus on one thing for 1-2 hours then play then focus again. He cannot do that as the class rotates every 30 min or so on things he already knows. The school does not fit his learning style nor what he wants to learn.
So, home school it is.
